Metrics and Grids

Devices vary not only in physical size, but also in screen density (DPI). To simplify the way you design for multiple screens, think of each device as
falling into a particular size bucket and density bucket:

The size buckets are handset (smaller than
600dp) and tablet (larger than or equal 600dp).

The density buckets are LDPI, MDPI, HDPI, XHDPI, and XXHDPI.

Optimize your application's UI by designing
alternative layouts for some of the different size buckets, and provide alternative bitmap images
for different density buckets.

Because it's important that you design and implement your layouts for multiple densities,
the guidelines below and throught the documentation
refer to layout dimensions with dp measurements instead of pixels.

Space considerations

Devices vary in the amount of density-independent pixels (dp) they can display.

48dp Rhythm

Touchable UI components are generally laid out along 48dp units.

Why 48dp?

On average, 48dp translate to a physical size of about 9mm (with some variability). This is
comfortably in the range of recommended target sizes (7-10 mm) for touchscreen objects and users
will be able to reliably and accurately target them with their fingers.

If you design your elements to be at least 48dp high and wide you can guarantee that:

your targets will never be smaller than the minimum recommended target size of 7mm regardless of
what screen they are displayed on.

you strike a good compromise between overall information density on the one hand, and
targetability of UI elements on the other.